I have used the Tungsol 6550 in the power supply of the Ref 3 for a couple of
weeks. I don't have a final word, but tentatively my thumb is down. The Tungsol gives
a very pleasing sound with a strong bass, luscious mids, and controlled treble. . . but
listening at length reveals that mids may be actually slightly bloated. Treble is probably
slightly depressed compared to the SED Winged. The end result is in my view a rather
romantic or euphonic presentation that is more nostalgic than real, lacking in complexity
and upper harmonic development. On the positive side, Tungsol might have slightly
more image specificity than the SED Winged. I have now reinstalled the SED Winged. I will conduct more tests with Tungsol on a recording that sounds somewhat etched using SED Winged: Dvorak complete strings quartets played by Panocha Quartet on Supraphon.
On a related note, I have also replaced all Sovtec 6H30s in the Ref 3. As I suspected, my
tubes were getting old at about 2200 hrs. Symptoms were reduced dynamics, reduced detail, colder sound, little etched. I am now getting
a sound that is significantly more involving and harmonically rich than what I have
experienced since early Summer 2007. 1800 hrs may be the extent that stock 6H30 tubes last in my Ref 3 before starting to decline. The new 6H30s are the EH 6H30PI "Gold" variant )(with gold plated contacts) that I have sourced from the TubeStore.